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Cast aluminum is a problematic material to weld. Part o […]
Cast aluminum is a problematic material to weld. Part of that is due to the material itself, and part is due to how cast aluminum is made. “You should never judge a book by its cover” is as apt here as anywhere; it’s tricky because even a brand-new, “clean” casting can be a pain in the ass, while a 100-year-old dull and dirty piece of cast aluminum could weld smooth as silk.My good friend Ralph is big into late ‘60s/early ‘70s Alfa Romeos.
I wanna say he’s on his third resto/build just in the last couple of years? On one of these cars the cast aluminum bell housing developed a pretty significant crack after an unfortunate fall to concrete during the installation. Ralph wasn’t sure how readily available these parts were and asked if it could be fixed. Could it be? I was pretty sure the answer was yes, but that’s only part of the equation.I remember a long while back working on another bell housing for a friend’s 1970 Charger. It was an oily mess, and at first glance my brain thought, “Man, this is gonna be a project!” I sprayed a little degreaser on it and wiped it down, heated it up with an oxyacetylene torch to burn out impurities, and sat down all geared up for battle.
The fight never materialized. It welded beautifully and took Carbon Steel Casting me maybe 10 minutes to fix. On the other hand, I’ve also welded on brand-new castings that cackle and snort and devolve into a series of little black volcanoes popping up where the bead should be.The crack in this Alfa housing was bad enough that it was gonna take a bit of finesse no matter the condition of the base metal.If a part is rare, difficult to find, or superexpensive, then attempting a repair makes sense. But if it’s readily available for a reasonable price, what I charge for the repair might push the cost high enough to not make sense. It might be better just to buy another one in good condition.
Ralph ended up finding a new one, but I told him to leave the cracked one with me and I’d see if I could fix it and document the process when I had the time.Why is cast aluminum so hit or miss? Aluminum, no matter its form, is very susceptible to contamination. Any bit of dirt complicates the welding, and it typically needs to be completely ground out to lay down a clean bead. It can spread like the black plague if you try to weld over it, and then it becomes harder to fix.The casting process adds issues you won’t find in other forms. It’s not going to be as dense as rolled or forged aluminum, so it’s a bit more porous by nature. It’s pretty common to hit air pockets and get some “popping” when TIG welding. Dirt can get trapped in pockets during the process as well. Because of this porous nature, if a casting has been exposed to oil or other fluids during use, chances are it’s seeped in, further complicating issues.